In an elevator hoisting machine, for example, a machinery brake that mechanically engages with a rotating part of the hoisting machine is normally used as a brake device. Structurally, the machinery brake can be e.g. a shoe brake, a drum brake or a disc brake.
The machinery brake generally comprises springs, which push a braking piece provided with a brake pad against the braking surface of a rotating part to brake the movement of the rotating part of the hoisting machine. A machinery brake generally also comprises an electromagnet, with which a braking piece provided with a magnetic core is pulled against the thrusting force of the springs into a releasing position of the brake away from the braking surface. The machinery brake is dropped by disconnecting the current supply of the electromagnet of the machinery brake, in which case the force of attraction of the electromagnet ceases and the springs in the brake push the braking piece provided with a brake pad from the initial position of the drop-out movement into the braking position against the braking surface of the rotating part.
During a run, current is connected to the electromagnet, in which case the braking piece is in the releasing position and the elevator car can move up or down in the elevator hoistway.
As the current of the electromagnet decreases, the thrusting force exerted by the spring finally exceeds the force of attraction of the electromagnet, and the braking piece displaces into the braking position. Owing to the imbalance of forces the brake pad strikes against the braking surface of the rotating part of the machine. When the brake opens, the electromagnet again exerts on the braking piece a force that is in the opposite direction to the thrusting force of the spring. When the force exerted on the braking piece by the electromagnet increases to be greater than the spring force, the air gap between the base part of the brake and the braking piece closes, and the armature part strikes against the base part.